This is the subject of probably 10% of the threads on /g/ :-)
I personally find the DT770 very disappointing. Their noise isolation
is superb, but they're one of the most colored closed cans in my
personal experience. HUGE midbass bump, no high end.
I'm not a fan of Sony overall, but the MDR-V6 is more neutral, cheaper
and better made. Amazon's been selling them for $50-- at that price,
they're a steal (I grabbed a few pairs myself).
BTW, If you don't need noise isolation, don't buy closed cans.
Monty